A case study on thrust bearing failures at the SÃO SIMÃO hydroelectric power plant

Abstract

After twenty years without any apparent problems on their combined guide and thrust bearings, the six 280MW hydrogenerators of the São Simão Hydroelectric Power Plant were failing. The source of the failure was the melting of the thrust pad babbitt lining. The machines began showing performance failures, leading to a sudden interruption in their operation. This caused considerable losses with high direct and indirect costs. The solution proposed by the bearing manufacturer was an improvement in the bearing design and the installation of new water–oil heat exchangers. The direct cost of their solution was estimated to be US $2,400,000.00. In a search for a less expensive alternative, CEMIG started a parallel study focused on the heat exchangers. A methodology based on heat transfer was applied, indicating that an increase in the heat exchange surface area could solve the problem. A third heat exchanger was added in one machine that already possessed two. The results fulfilled the preliminary predictions, eliminating the risk of additional babbitt lining failures. As a consequence of this success modeling, heat exchangers were replaced by stainless steel plate ones in all machines. This alternative solution had a total direct cost of US $600,000.00.